In recent years, there have been remarkable progresses in magnetic recording technology, and heightening of recording densities in magnetic recording media has been preceding due to increasing drive capacities. For example, perpendicular magnetic recording system, which achieves further high recording density when compared to longitudinal magnetic recording system conventionally used, has been put into practical use. Perpendicular magnetic recording system is a system in which a magnetization-easy axis is oriented in the direction vertical to the medium surface of a magnetic film of a perpendicular magnetic recording medium and is suitable for a high recording density. For perpendicular magnetic recording system, a double-layer recording medium having a magnetic recording film layer with an increased recording sensitivity and a soft magnetic film layer has been developed. For the magnetic recording film layer, a CoCrPt—SiO2-based alloy is commonly used.
As for a conventional soft magnetic film layer, ferromagnetism and amorphous properties are necessary and, in addition, various properties, such as a high saturation magnetic flux density, high corrosion resistance, and a high hardness, are additionally required depending on applications of perpendicular magnetic recording media and environments in which they are used. For example, as disclosed in Japanese Patent Laid-Open Publication No. 2008-260970 (Patent Literature 1), there are used substances which are based on Co, a ferromagnetic element with high corrosion resistance, and to which amorphization promotion elements including Zr are added to enhance amorphous properties.
As disclosed in Japanese Patent Laid-Open Publication No. 2008-299905 (Patent Literature 2), the addition of Fe results in high saturation magnetic flux density and the addition of B results in high hardness. Furthermore, in recent years, there have been required alloys for soft magnetic films having a low coercive force as well as the conventionally required properties described above.